Why use hair instead of emitter as particles?
If you use the Hair particle then a fixed number of particles will be created and their number and position won't change over time as your animation plays. So this is good for hair, sprinkles, or grass.

If you use the Emitter, the number of partciles will change over time. So if you play your animation, you'll see the object starts emitting particles that move away from your object and then disappear. You would use an emitter more for water, smoke, or sparks.

For demonstration, look at how the emitters of these 2 cubes change while the animation is playing. The one on the left uses Hair, the one on the right uses Emitter.